G23A-01 INVITED
Requirements for an L-band InSAR Mission to Monitor Global Tectonic Activities
DLR is currently studying a space mission based on a formation of two L-band Synthetic Aperture Radar satellites dedicated to monitor a) the global biomass for CO2 cycle studies b) small displacements of the earth surface. The focus of this presentation is the so called deformation mode for repeated displacement measurements during the mission lifetime. Measurements shall be made on risk regions such as faults, volcanoes, landslides and urban areas – or even globally if feasible. The study is currently in the requirements definition phase where the following parameters are discussed with the scientific user community, most importantly: - signal characteristics & accuracy requirements, - areas of interest, - revisit time requirements for different application fields such as volcanic or seismic activity, landslides or anthropogenic subsidence and - definition product levels, i.e., different processing stages. The goal of the study is to design a mission optimized for the derived requirements. This includes - mission & coverage concepts, - instrument design and - 3D motion reconstruction methods. In our presentation we show the current ideas and the requirements collected for deformation measurements.
G23A-02
Glacier acceleration, glacial earthquakes, and ice loss at Helheim Glacier, Greenland
Satellite observations during the last decade have shown dramatic changes in flow speed at Greenland's outlet glaciers, often accompanied by retreats of several km in calving-front location and increasing numbers of glacial earthquakes. Geodetic, seismological, and oceanographic data collected as part of a multidisciplinary field experiment at Helheim Glacier, East Greenland, over three summer seasons (2006--2008), together with satellite imagery, place new constraints on the processes responsible for these changes. Analysis of high-rate GPS data from 2007 reveals several large, sudden increases in flow speed at Helheim Glacier. These abrupt accelerations are detected along the length of the glacier (~20~km) spanned by the GPS network, and coincide in time with major calving events and teleseismically detected glacial earthquakes. The calving events are implicated in the earthquake source process. Further, our results link changes in glacier velocity directly to calving-front behavior at Greenland's large outlet glaciers, on timescales as short as minutes to hours. No large earthquakes occurred at Helheim Glacier during the 2006 field campaign, providing the opportunity for comparison between seismically active and quiescent modes of glacier behavior. Data recorded in 2008 include near-field broadband seismic recordings and time-lapse photography, allowing us to refine our understanding of both the glacial earthquake source process and the glacier response to major ice loss events.
G23A-03 INVITED
InSAR Measurement of Ice Sheet Motion: A Current and Future Perspective
Spaceborne synthetic aperture radars (SAR) have collected data over the Greenland and Antarctic ice sheets for nearly fifteen years. Interferometric SAR and speckle tracking programs running on low cost computers have evolved to the point where it now is possible to measure velocity over vast areas of the ice sheet. Numerous studies using these data have revealed major changes in ice sheet flow, which were entirely unanticipated prior to the launch of ERS-1. To demonstrate existing capabilities, we describe a systematic mapping effort currently underway to provide annual estimates of ice velocity for the Greenland Ice Sheet using fine-beam RADARSAT and Terra-SAR-X. We also describe areas of West Antarctica where velocity has been measured using a combination of ERS and RADARSAT data. These data sets reveal both the strengths and weaknesses of existing C-band sensors, which were not specifically designed for interferometry. While current and many planned missions provide important mapping capability, they are not optimized for InSAR and fall far short of what could be measured. Thus, a dedicated the DESDynI InSAR mission that will be specifically optimized for interferometry will provide a critical new means for determining ice-sheet response to climate change.
G23A-04
Measurement Capabilities and Expected Performance of the DESDynI Multi-beam Lidar
The DESDynI mission consists of a Full-waveform Multi-beam Lidar and a Synthetic Aperture Radar for measuring Surface Deformation, Vegetation Structure, and Ice Sheets. Although the primary purpose of the Multi-beam Lidar is ecosystem structure, this Lidar system will also make significant contributions to a variety of other science applications. The current baseline design for the DESDynI Lidar has 5 beams each operating at a repetition rate of 240 Hz. After 5 years of operations, the Lidar will produce approximately 20- 30 Billion land and ice surface measurements with an extraordinary number of track crossings that can be used to directly assess surface change. Analysis of the performance of the Laser Vegetation Imaging Sensor (LVIS) that utilizes a similar laser pulsewidth and footprint diameter (i.e., 20-25 m) has shown 3 cm range precision for altimetric purposes. Coupling this precise ranging capability with a highly accurate attitude determination system and position determination system results in sub-decimeter accuracy measurements of land and ice surface topography. The results of numerical simulations and LVIS data analysis will be used to estimate the expected performance of the DESDynI Lidar in space. Performance under a variety of surface slope, reflectivity, and roughness conditions will be assessed.
G23A-05 INVITED
A multiscale approach to InSAR time series analysis
We describe a new technique to constrain time-dependent deformation from repeated satellite-based InSAR observations of a given region. This approach, which we call MInTS (Multiscale analysis of InSAR Time Series), relies on a spatial wavelet decomposition to permit the inclusion of distance based spatial correlations in the observations while maintaining computational tractability. This approach also permits a consistent treatment of all data independent of the presence of localized holes in any given interferogram. In essence, MInTS allows one to considers all data at the same time (as opposed to one pixel at a time), thereby taking advantage of both spatial and temporal characteristics of the deformation field. In terms of the temporal representation, we have the flexibility to explicitly parametrize known processes that are expected to contribute to a given set of observations (e.g., co-seismic steps and post-seismic transients, secular variations, seasonal oscillations, etc.). Our approach also allows for the temporal parametrization to includes a set of general functions (e.g., splines) in order to account for unexpected processes. We allow for various forms of model regularization using a cross-validation approach to select penalty parameters. The multiscale analysis allows us to consider various contributions (e.g., orbit errors) that may affect specific scales but not others. The methods described here are all embarrassingly parallel and suitable for implementation on a cluster computer. We demonstrate the use of MInTS using a large suite of ERS-1/2 and Envisat interferograms for Long Valley Caldera, and validate our results by comparing with ground-based observations.
G23A-06
Time Series of Deformation in Southern California From 15 Years of InSAR Observations
We present time series of line-of-sight (LOS) displacements derived from the Synthetic Aperture Radar
(SAR) data collected over the Southern San Andreas Fault System. We use data acquired by the ERS
satellites from the descending tracks 127 and 356 over a time period between 1992 and 2007. For each
coherent pixel of the radar images we compute time-dependent surface displacements as well as an average
LOS velocity. We compare the mean LOS velocity fields calculated using the Small BAseline Subset
Algorithm (SBAS) and Atmospheric Noise Reduction (ANR) scheme. The velocity fields inferred using the two
methods are in excellent agreement, suggesting that estimates of time-dependent deformation are robust.
The inferred LOS velocity fields also favorably compare to the continuous GPS data (projected onto the
satellite line of sight). However, we find that velocity estimates obtained without orbital corrections have small
but systematic biases compared to GPS data. This implies that orbital errors are not randomly distributed
throughout the history of radar acquisitions, and auxiliary data (e.g., tie points using GPS-derived velocities)
may be necessary for correcting the effects of imprecise satellite orbits. We use the dense InSAR and GPS
time series to investigate interseismic deformation rates due to major faults of the Southern San Andreas
system. We model the new InSAR and available GPS data to constrain secular slip rates on major faults, as
well as to detect and quantify any possible transient slip.
http://sioviz.ucsd.edu/~fialko
G23A-07 INVITED
InSAR time-series: Results from Kilauea volcano, Hawaii, and the Eastern California Shear Zone.
With up to 100-150 SAR images acquired for many places since 1992 the InSAR technique has developed in the past years from the typical one-interferogram approach to time-series approaches relying on the simultaneous analysis of all available acquisitions. The advantage of the time-series methods are that (1) the variability of ground deformation with time can be resolved, (2) subtle deformation of the order of a few mm/yr can be recovered by averaging over long time periods, (3) phase contributions due to errors associated with the satellite orbits used for the processing can be largely eliminated. This is particularly important for imagery acquired by the Radarsat-1 satellite for which no precise orbit information is available. We present example of time-series analysis for the Eastern California Shear zone and for Hawaii. In the ECSZ we use InSAR to resolve the deformation across the Hunter Mountain fault. In Hawaii we use InSAR time series to illuminate the shallow plumbing system of Kilauea volcano. These examples illustrate the importance of frequent SAR acquisitions.
G23A-08
Impact of InSAR Sampling Interval on Discrimination of Postseismic Processes
In order to understand the impact of InSAR sampling interval on the discrimination of postseismic processes we generate time dependent postseismic surface deformation with 1 cm error from an ensemble of synthetic earthquakes. We study a linear combination of logarithmic afterslip and exponential decay relaxation. Coseismic and postseismic slip and the time constants for postseismic processes were generated from random distributions based on published postseismic parameters. A time series with parameter partials was generated for each synthetic event and transformed into estimation errors. We consider a synthetic event to be successfully resolved if the estimated amplitudes for both afterslip and relaxation have formal relative error less than half the larger of the two amplitudes. For two years of observations following an event, using an 8-day repeat as the nominal design we lose 5 per cent of the resolved events by changing to a 14 day repeat, and 19 per cent by changing to a 45 day repeat. If we consider a half-year observation time and 8 day repeat, we will fail to resolve 58 per cent of the nominal resolved cases, 65 per cent for 14 day repeat, and 88 percent for a 45 day repeat.